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commercial fleets, the majority at 60-90 ft. (18 – 28 m),
head out to sea off the coasts of Alaska and Canada in
some of the worst weather imaginable. These single-screw
displacement vessels venture many miles out into open
ocean year after year. Many have been converted to pleas-
ure craft, some with more success than others. The baby-
boomers with their high-tech interests are intrigued by, and
look for, innovation - as long as it is backed up by solid engi-
neering. Many have earned their retirement funds from the
technology and dot-com industries and see innovation as a
part of their everyday life.
Hull Design:
This hull design work started with a paper study on various
published hull forms, their relative efficiencies and seawor-
thiness. Standard resistance curves for a wide variety of
displacement, semi-displacement, and planing hulls were
studied to establish their “sweet spots” and how this applied
to the speed/length ratios that had been targeted. Out of
this analysis came the decision to use a lobster boat type of
hull, as it was considered to be the most efficient over this
range of speed (√LWL x 0.9 to 2.3).
From here, various features were added to further enhance
performance; a finer bow for low resistance and low bow
wave, but high, wide spray knockers to add significant vol-
ume when pitching into a seaway; low transom immersion
to reduce drag at low speeds, and wide spray chines above
the waterline to give trim control at higher speeds. (Fig. 1
Fox 86, Config. A, previous page)
With the addition of performance enhancing appendages
this work saw gains of up to 30% in efficiency and has been
incorporated into vessels without having to resort to unat-
tractive styling or stealth-style lines. In fact, this contempo-
rary styling makes these boats real sleepers, disguising their
efficiency to the point that their abilities are often disbe-
lieved even with reality floating right there at the dock.
At 6 knots with this hull shape and appendage combination,
there is no noticeable wave train. At 15 knots, there is con-
siderably less wave than most moderate-displacement
trawlers. (Fig. 2) At 20 knots, this form is equal to chined,
fully planing forms for resistance and wave profile.
APPENDAGES
Bulbous Bow:
The bulb design work was inspired by the work of Dr. Cali
of the University of British Columbia who did extensive st
ies on the application of bulbous bows on fish boats in th
early nineteen-eighties. From his published work with the
fishing vessel “Kynok” a refined concept has been develo
ing that results in a bulb design that is effective from 8-2
knots and produces a drop in resistance of over 11% at it
maximum efficiency. In retrofitting bulbs to over 36 exist
vessels, over the past six years, it was found that the atta
ment of a bulb would produce an immediate 3/4 knot in-
crease in speed, or a minimum 10% fuel savings.
A quote from a recent model-test program for the Fox 86
footer states,
“From the Resistance and EHP plots it is ev
dent that the bulb reduces the required power throughout
the range of speeds from 9 to 19 knots, with crossover at
knots. The reduction is accomplished through wave canc
tion and by reduction of the running trim due to the hydro
namic forces acting on the bulb.”
In addition to these fue
savings there is close to 50% reduction in pitching motio
but more on that once the other appendages have been
cussed.
Bi-Foil Skeg:
Another piece of technology inspired by work developed f
the fishing fleets is the “bi-foil skeg” (Fig.3). Its evolution
a paper in itself but suffice it to say that it came about
through drag reduction technology applied to the pipe fra
net guard, typically called a “beaver bail,” fitted under th
propeller on fishing seiners. By optimizing the plan form
and utilizing a proper hydrodynamic foil section it is possi
to reduce drag and increase propeller thrust. This is don
driving water to the prop and loading it up with clean, tur
lence free water. The foil shape also acts as an automati
trim device. As the stern-down trim increases, the angle
attack on the foil increases creating more lift. This lift th
reduces the running trim and dampens out the pitching
tions at the stern as well. At the same time the prop is
Continued next p
Fig. 2 Cape Scott 86 at 15 knots
Fig. 3 Bi-foil Skeg